Microfabrication by lithography in which photoresist compositions are used is a technology conventionally resorted to in semiconductor device production. The abovementioned microfabrication is a processing method that involves forming a thin film of a photoresist composition on a substrate to be processed, for instance a silicon wafer, irradiating actinic rays, such as ultraviolet rays, onto the thin film of the photoresist composition via a mask pattern in which there is drawn a pattern of the semiconductor device, developing the pattern, and etching the substrate to be processed, such as a silicon wafer, using the obtained photoresist pattern as a protective film. Ever higher integration in semiconductor devices in recent years has been matched by a trend towards shorter wavelengths in the actinic rays that are utilized, from KrF excimer lasers (248 nm) to ArF excimer lasers (193 nm). This shift to shorter wavelengths has been accompanied by significant problems, namely standing waves and diffuse reflection of the actinic rays off the substrate. Accordingly, methods have been extensively studied that involve providing an anti-reflective coating (Bottom Anti-Reflective Coating, BARC) between the photoresist and the substrate to be processed.
Thinner resists have become desirable as a response to the problems of resolution and resist pattern collapse after development that arise as resist patterns become ever thinner. Accordingly, achieving sufficient resist pattern thickness for substrate processing was difficult, and thus processes have become necessary in which the function of a mask during substrate processing is imparted not only to the resist pattern, but also to a resist underlayer film that is produced between the resist and the semiconductor substrate to be processed. Such resist underlayer films for processing that are now required include resist underlayer films for lithography having a selection ratio of dry etching rate close to that of the resist, resist underlayer films for lithography having a selection ratio of dry etching rate smaller than that of the resist, and resist underlayer films for lithography having a selection ratio of dry etching rate smaller than that of the semiconductor substrate, which are different from conventional resist underlayer films having high etch rate (high etching rate).
Examples of polymers for the abovementioned resist underlayer films include, for instance, the following.
Compositions for forming a resist underlayer film that utilize polyvinyl carbazole (Patent Document 1, Patent Document 2 and Patent Document 3).
Compositions for forming a resist underlayer film that utilize a fluorene phenol novolac resin (for instance, Patent Document 4).
Compositions for forming a resist underlayer film that utilize a fluorene naphthol novolac resin (for instance, Patent Document 5).
Compositions for forming a resist underlayer film that include a resin having repeating units of fluorene phenol and an arylalkylene (for instance, Patent Document 6 and Patent Document 7).